Concrete is the most consumed man-made material in the world. A typical concrete is made by mixing Portland cement, water and aggregates such as sand and crushed stone. Portland cement is a synthetic material made by burning a mixture of ground limestone and clay, or materials of similar composition in a rotary kiln at a sintering temperature of 1450° C. Portland cement manufacturing is not only an energy-intensive process, but one which releases considerable quantities of greenhouse gas (CO2). The cement industry accounts for approximately 5% of global anthropogenic CO2 emissions. More than 60% of this CO2 comes from the chemical decomposition, or calcination of limestone.
There has been a growing effort to reduce total CO2 emissions within the cement industry. According to a proposal by the International Energy Agency, the cement industry needs to reduce its CO2 emissions from 2.0 Gt in 2007 to 1.55 Gt by 2050. This represents a daunting task because, over this same period, cement production is projected to grow from 2.6 Gt to 4.4 Gt.
To meet this challenge, a revolutionary approach to cement production is required that significantly reduces the energy requirement and CO2 emissions of a cement plant. Ideally, the new approach preferably offers the ability to permanently and safely sequester CO2 while being adaptable and flexible in equipment and production requirements, allowing manufacturers of conventional cement to easily convert to the new platform.
Carbonatable calcium silicate cements provide a foundation for a revolutionary approach to cement production that significantly reduces the energy requirement and CO2 emissions. Carbonatable calcium silicate cements are suitable for use as non-hydraulic cement that hardens by a carbonation process and may be applied in a variety of concrete components in the infrastructure, construction, pavement and landscaping industries. Challenges remain, however, in the effort to realize the full potential of carbonatable calcium silicate-based cement technology. For instance, improvements are desired that can effectively control cement setting in order to take full advantage of the promising non-hydraulic and non-setting cement technology.